Perl::Critic is an extensible framework for creating and applying coding standards to Perl source code. Essentially, it is a static source code analysis engine. Perl::Critic is distributed with a number of Perl::Critic::Policy modules that attempt to enforce various coding guidelines. Most Policy modules are based on Damian Conway's book Perl Best Practices. However, Perl::Critic is not limited to PBP and will even support Policies that contradict Conway. You can enable, disable, and customize those Polices through the Perl::Critic interface. You can also create new Policy modules that suit your own tastes.

For a command-line interface to Perl::Critic, see the documentation for perlcritic. If you want to integrate Perl::Critic with your build process, Test::Perl::Critic provides an interface that is suitable for test programs. Also, Test::Perl::Critic::Progressive is useful for gradually applying coding standards to legacy code. For the ultimate convenience (at the expense of some flexibility) see the criticism pragma.

If you'd like to try Perl::Critic without installing anything, there is a web-service available at http://perlcritic.com. The web-service does not yet support all the configuration features that are available in the native Perl::Critic API, but it should give you a good idea of what it does. You can also invoke the perlcritic web-service from the command-line by doing an HTTP-post, such as one of these:

Returns a reference to a new Perl::Critic object. Most arguments are just passed directly into Perl::Critic::Config, but I have described them here as well. The default value for all arguments can be defined in your .perlcriticrc file. See the "CONFIGURATION" section for more information about that. All arguments are optional key-value pairs as follows:

-profile is a path to a configuration file. If $FILE is not defined, Perl::Critic::Config attempts to find a .perlcriticrc configuration file in the current directory, and then in your home directory. Alternatively, you can set the PERLCRITIC environment variable to point to a file in another location. If a configuration file can't be found, or if $FILE is an empty string, then all Policies will be loaded with their default configuration. See "CONFIGURATION" for more information.

-severity is the minimum severity level. Only Policy modules that have a severity greater than $N will be applied. Severity values are integers ranging from 1 (least severe violations) to 5 (most severe violations). The default is 5. For a given -profile, decreasing the -severity will usually reveal more Policy violations. You can set the default value for this option in your .perlcriticrc file. Users can redefine the severity level for any Policy in their .perlcriticrc file. See "CONFIGURATION" for more information.

If it is difficult for you to remember whether severity "5" is the most or least restrictive level, then you can use one of these named values:

The names reflect how severely the code is criticized: a gentle criticism reports only the most severe violations, and so on down to a brutal criticism which reports even the most minor violations.

-theme is special expression that determines which Policies to apply based on their respective themes. For example, the following would load only Policies that have a 'bugs' AND 'pbp' theme:

my $critic = Perl::Critic->new( -theme => 'bugs && pbp' );

Unless the -severity option is explicitly given, setting -theme silently causes the -severity to be set to 1. You can set the default value for this option in your .perlcriticrc file. See the "POLICY THEMES" section for more information about themes.

-include is a reference to a list of string @PATTERNS. Policy modules that match at least one m/$PATTERN/ixms will always be loaded, irrespective of all other settings. For example:

This would cause Perl::Critic to apply all the CodeLayout::* Policy modules even though they have a severity level that is less than 4. You can set the default value for this option in your .perlcriticrc file. You can also use -include in conjunction with the -exclude option. Note that -exclude takes precedence over -include when a Policy matches both patterns.

-exclude is a reference to a list of string @PATTERNS. Policy modules that match at least one m/$PATTERN/ixms will not be loaded, irrespective of all other settings. For example:

This would cause Perl::Critic to not apply the RequireUseStrict and ProhibitNoStrict Policy modules even though they have a severity level that is greater than 1. You can set the default value for this option in your .perlcriticrc file. You can also use -exclude in conjunction with the -include option. Note that -exclude takes precedence over -include when a Policy matches both patterns.

-single-policy is a string PATTERN. Only one policy that matches m/$PATTERN/ixms will be used. Policies that do not match will be excluded. This option has precedence over the -severity, -theme, -include, -exclude, and -only options. You can set the default value for this option in your .perlcriticrc file.

-top is the maximum number of Violations to return when ranked by their severity levels. This must be a positive integer. Violations are still returned in the order that they occur within the file. Unless the -severity option is explicitly given, setting -top silently causes the -severity to be set to 1. You can set the default value for this option in your .perlcriticrc file.

-only is a boolean value. If set to a true value, Perl::Critic will only choose from Policies that are mentioned in the user's profile. If set to a false value (which is the default), then Perl::Critic chooses from all the Policies that it finds at your site. You can set the default value for this option in your .perlcriticrc file.

-force is a boolean value that controls whether Perl::Critic observes the magical "## no critic" annotations in your code. If set to a true value, Perl::Critic will analyze all code. If set to a false value (which is the default) Perl::Critic will ignore code that is tagged with these annotations. See "BENDING THE RULES" for more information. You can set the default value for this option in your .perlcriticrc file.

-verbose can be a positive integer (from 1 to 11), or a literal format specification. See Perl::Critic::Violation for an explanation of format specifications. You can set the default value for this option in your .perlcriticrc file.

-unsafe directs Perl::Critic to allow the use of Policies that are marked as "unsafe" by the author. Such policies may compile untrusted code or do other nefarious things.

-color and -pager are not used by Perl::Critic but is provided for the benefit of perlcritic.

-criticism-fatal is not used by Perl::Critic but is provided for the benefit of criticism.

-color-severity-highest, -color-severity-high, -color-severity-medium, -color-severity-low, and -color-severity-lowest are not used by Perl::Critic, but are provided for the benefit of perlcritic. Each is set to the Term::ANSIColor color specification to be used to display violations of the corresponding severity.

-files-with-violations and -files-without-violations are not used by Perl::Critic, but are provided for the benefit of perlcritic, to cause only the relevant filenames to be displayed.

Runs the $source_code through the Perl::Critic engine using all the Policies that have been loaded into this engine. If $source_code is a scalar reference, then it is treated as a string of actual Perl code. If $source_code is a reference to an instance of PPI::Document, then that instance is used directly. Otherwise, it is treated as a path to a local file containing Perl code. This method returns a list of Perl::Critic::Violation objects for each violation of the loaded Policies. The list is sorted in the order that the Violations appear in the code. If there are no violations, this method returns an empty list.

Creates a Policy object and loads it into this Critic. If the object cannot be instantiated, it will throw a fatal exception. Otherwise, it returns a reference to this Critic.

-policy is the name of a Perl::Critic::Policy subclass module. The 'Perl::Critic::Policy' portion of the name can be omitted for brevity. This argument is required.

-params is an optional reference to a hash of Policy parameters. The contents of this hash reference will be passed into to the constructor of the Policy module. See the documentation in the relevant Policy module for a description of the arguments it supports.

For those folks who prefer to have a functional interface, The critique method can be exported on request and called as a static function. If the first argument is a hashref, its contents are used to construct a new Perl::Critic object internally. The keys of that hash should be the same as those supported by the Perl::Critic::new method. Here are some examples:

Most of the settings for Perl::Critic and each of the Policy modules can be controlled by a configuration file. The default configuration file is called .perlcriticrc. Perl::Critic will look for this file in the current directory first, and then in your home directory. Alternatively, you can set the PERLCRITIC environment variable to explicitly point to a different file in another location. If none of these files exist, and the -profile option is not given to the constructor, then all the modules that are found in the Perl::Critic::Policy namespace will be loaded with their default configuration.

The format of the configuration file is a series of INI-style blocks that contain key-value pairs separated by '='. Comments should start with '#' and can be placed on a separate line or after the name-value pairs if you desire.

Default settings for Perl::Critic itself can be set before the first named block. For example, putting any or all of these at the top of your configuration file will set the default value for the corresponding constructor argument.

Perl::Critic::Policy::Category::PolicyName is the full name of a module that implements the policy. The Policy modules distributed with Perl::Critic have been grouped into categories according to the table of contents in Damian Conway's book Perl Best Practices. For brevity, you can omit the 'Perl::Critic::Policy' part of the module name.

severity is the level of importance you wish to assign to the Policy. All Policy modules are defined with a default severity value ranging from 1 (least severe) to 5 (most severe). However, you may disagree with the default severity and choose to give it a higher or lower severity, based on your own coding philosophy. You can set the severity to an integer from 1 to 5, or use one of the equivalent names:

The names reflect how severely the code is criticized: a gentle criticism reports only the most severe violations, and so on down to a brutal criticism which reports even the most minor violations.

set_themes sets the theme for the Policy and overrides its default theme. The argument is a string of one or more whitespace-delimited alphanumeric words. Themes are case-insensitive. See "POLICY THEMES" for more information.

add_themes appends to the default themes for this Policy. The argument is a string of one or more whitespace-delimited words. Themes are case-insensitive. See "POLICY THEMES" for more information.

maximum_violations_per_document limits the number of Violations the Policy will return for a given document. Some Policies have a default limit; see the documentation for the individual Policies to see whether there is one. To force a Policy to not have a limit, specify "no_limit" or the empty string for the value of this parameter.

The remaining key-value pairs are configuration parameters that will be passed into the constructor for that Policy. The constructors for most Policy objects do not support arguments, and those that do should have reasonable defaults. See the documentation on the appropriate Policy module for more details.

Instead of redefining the severity for a given Policy, you can completely disable a Policy by prepending a '-' to the name of the module in your configuration file. In this manner, the Policy will never be loaded, regardless of the -severity given to the Perl::Critic constructor.

A simple configuration might look like this:

#--------------------------------------------------------------
# I think these are really important, so always load them
[TestingAndDebugging::RequireUseStrict]
severity = 5
[TestingAndDebugging::RequireUseWarnings]
severity = 5
#--------------------------------------------------------------
# I think these are less important, so only load when asked
[Variables::ProhibitPackageVars]
severity = 2
[ControlStructures::ProhibitPostfixControls]
allow = if unless # My custom configuration
severity = cruel # Same as "severity = 2"
#--------------------------------------------------------------
# Give these policies a custom theme. I can activate just
# these policies by saying `perlcritic -theme larry`
[Modules::RequireFilenameMatchesPackage]
add_themes = larry
[TestingAndDebugging::RequireTestLables]
add_themes = larry curly moe
#--------------------------------------------------------------
# I do not agree with these at all, so never load them
[-NamingConventions::Capitalization]
[-ValuesAndExpressions::ProhibitMagicNumbers]
#--------------------------------------------------------------
# For all other Policies, I accept the default severity,
# so no additional configuration is required for them.

For additional configuration examples, see the perlcriticrc file that is included in this examples directory of this distribution.

Damian Conway's own Perl::Critic configuration is also included in this distribution as examples/perlcriticrc-conway.

A large number of Policy modules are distributed with Perl::Critic. They are described briefly in the companion document Perl::Critic::PolicySummary and in more detail in the individual modules themselves. Say "perlcritic -doc PATTERN" to see the perldoc for all Policy modules that match the regex m/PATTERN/ixms

There are a number of distributions of additional policies on CPAN. If Perl::Critic doesn't contain a policy that you want, some one may have already written it. See the "SEE ALSO" section below for a list of some of these distributions.

Each Policy is defined with one or more "themes". Themes can be used to create arbitrary groups of Policies. They are intended to provide an alternative mechanism for selecting your preferred set of Policies. For example, you may wish disable a certain subset of Policies when analyzing test programs. Conversely, you may wish to enable only a specific subset of Policies when analyzing modules.

The Policies that ship with Perl::Critic have been broken into the following themes. This is just our attempt to provide some basic logical groupings. You are free to invent new themes that suit your needs.

THEME DESCRIPTION
--------------------------------------------------------------------------
core All policies that ship with Perl::Critic
pbp Policies that come directly from "Perl Best Practices"
bugs Policies that that prevent or reveal bugs
maintenance Policies that affect the long-term health of the code
cosmetic Policies that only have a superficial effect
complexity Policies that specificaly relate to code complexity
security Policies that relate to security issues
tests Policies that are specific to test programs

Any Policy may fit into multiple themes. Say "perlcritic -list" to get a listing of all available Policies and the themes that are associated with each one. You can also change the theme for any Policy in your .perlcriticrc file. See the "CONFIGURATION" section for more information about that.

Using the -theme option, you can create an arbitrarily complex rule that determines which Policies will be loaded. Precedence is the same as regular Perl code, and you can use parentheses to enforce precedence as well. Supported operators are:

Perl::Critic takes a hard-line approach to your code: either you comply or you don't. In the real world, it is not always practical (nor even possible) to fully comply with coding standards. In such cases, it is wise to show that you are knowingly violating the standards and that you have a Damn Good Reason (DGR) for doing so.

To help with those situations, you can direct Perl::Critic to ignore certain lines or blocks of code by using annotations:

The "## no critic" annotations direct Perl::Critic to ignore the remaining lines of code until a "## use critic" annotation is found. If the "## no critic" annotation is on the same line as a code statement, then only that line of code is overlooked. To direct perlcritic to ignore the "## no critic" annotations, use the --force option.

A bare "## no critic" annotation disables all the active Policies. If you wish to disable only specific Policies, add a list of Policy names as arguments, just as you would for the "no strict" or "no warnings" pragmas. For example, this would disable the ProhibitEmptyQuotes and ProhibitPostfixControls policies until the end of the block or until the next "## use critic" annotation (whichever comes first):

The argument list must be enclosed in parentheses and must contain one or more comma-separated barewords (e.g. don't use quotes). The "## no critic" annotations can be nested, and Policies named by an inner annotation will be disabled along with those already disabled an outer annotation.

Some Policies like Subroutines::ProhibitExcessComplexity apply to an entire block of code. In those cases, "## no critic" must appear on the line where the violation is reported. For example:

Policies such as Documentation::RequirePodSections apply to the entire document, in which case violations are reported at line 1.

Use this feature wisely. "## no critic" annotations should be used in the smallest possible scope, or only on individual lines of code. And you should always be as specific as possible about which Policies you want to disable (i.e. never use a bare "## no critic"). If Perl::Critic complains about your code, try and find a compliant solution before resorting to this feature.

Coding standards are deeply personal and highly subjective. The goal of Perl::Critic is to help you write code that conforms with a set of best practices. Our primary goal is not to dictate what those practices are, but rather, to implement the practices discovered by others. Ultimately, you make the rules -- Perl::Critic is merely a tool for encouraging consistency. If there is a policy that you think is important or that we have overlooked, we would be very grateful for contributions, or you can simply load your own private set of policies into Perl::Critic.

The modular design of Perl::Critic is intended to facilitate the addition of new Policies. You'll need to have some understanding of PPI, but most Policy modules are pretty straightforward and only require about 20 lines of code. Please see the Perl::Critic::DEVELOPER file included in this distribution for a step-by-step demonstration of how to create new Policy modules.

If you develop any new Policy modules, feel free to send them to <jeff@imaginative-software.com> and I'll be happy to put them into the Perl::Critic distribution. Or if you would like to work on the Perl::Critic project directly, check out our repository at http://perlcritic.tigris.org. To subscribe to our mailing list, send a message to mailto:dev-subscribe@perlcritic.tigris.org.

The Perl::Critic team is also available for hire. If your organization has its own coding standards, we can create custom Policies to enforce your local guidelines. Or if your code base is prone to a particular defect pattern, we can design Policies that will help you catch those costly defects before they go into production. To discuss your needs with the Perl::Critic team, just contact <jeff@imaginative-software.com>.